I'm not sure what the etiquette is about "me too" comments in this Bugzilla instance, but I see the same behavior on a Lenovo Thinkpad T440s: /sys/class/backlight/intel_backlight is present but xbacklight simply says "No outputs have backlight property" when I try to run it. I have not installed the intel driver so I'm using modesetting by default.

I wonder if anyone of the developers is reading here at all?
The only reason not to use the modesetting driver is the missing backlight capability - as it is faster and more reliable than the intel driver (for intel hardware!).

(In reply to nico-freedesktop.org from comment #8)
> I wonder if anyone of the developers is reading here at all?
Martin's soon back from vacation.
I don't see Jani on the CC, but if this needs new API from kernel, bug about that should be linked here. Is there one?
> The only reason not to use the modesetting driver is the missing backlight
> capability - as it is faster and more reliable than the intel driver (for
> intel hardware!).
You didn't mention in which use-case, on which distro and with which exact HW you've compared modesetting and Intel DDX performance, but in our tests Intel DDX has been somewhat faster on average. As to reliability, there have been issues with DRI3, but those have been fixed in X libraries, Mesa, Intel DDX etc. Mainly you need to use new enough (full) stack.

This bug is also a problem for Wayland. The proper fix is to export a new property (backlight) attached to the DRM connector object and let the userspace deal with this. Once this lands, modesetting could be accessing it.
Now, if older distros require modesetting to work, we would need to port the workaround found in the intel ddx, but it really is a workaround and I would rather avoid adding this code in X, so it could live as an external patch.

(In reply to Eugen Dedu from comment #11)
> Hi,
>
> Is there any progress on this bug? xorg-server 1.19 is being released, is
> this bug too risky to fix for the oncoming release?
We have a patch series on the kernel side that is being polished right now. This introduces a backlight property on connectors and basically allow using the KMS interface to control the backlight.
In the coming days, we will start implementing support for it in the modesetting driver and everything should just work at this point. This is the cleanest design we could think of even though the kernel side is way more complex than it used to be.
Do not expect this feature to be ready before Linux 4.11 though :s We may work on a workaround in the mean time, but I am not sure this will be worth the effort. Stable distros could backport the patchset if they care.

Thanks for reporting the status.
For me it is somewhat disappointing that a feature like this breaks and stays broken for such a long time. If a workaround can be provided to fill the get I would very much appreciate it.
Meanwhile, I would just like to add a reference here to the Fedora/RedHat bugzilla where some more people have reported probably the same issue:
https://bugzilla.redhat.com/show_bug.cgi?id=1354662

In my case, I was using xbacklight in awesome WM to change screen backlight. Noticing that it is not going to be fixed soon, I replaced xbacklight command with an echo XYZ >/sys/class/backlight/intel_backlight/brightness, and added a chmod go+w /sys/class/backlight/intel_backlight/brightness in /etc/rc.local so that I, as a non-root user, can modify that file.

On Debian (Buster), there is a package, brightness-udev, which includes only the udev scripts of brightnessctl (scripts to allow users of video group to manage brightness and input group manage leds).
Installing this package avoids the need to modify system files (like /etc/rc.local noted above). Also, brightnessctl works to control the backlight in this case.

Fyi - I just wrote cbacklight to cleanly / easily fix this problem:
[14:21] line:~% cbacklight --help
usage: cbacklight [-h] [--inc INC | --dec DEC | --set SET] [--get]
cbacklight
optional arguments:
-h, --help show this help message and exit
--inc INC Increment by percentage (points)
--dec DEC Decrement by percentage (points)
--set SET Set to percentage
--get Get percentage (default)
[14:21] line:~% cbacklight --inc 5
[14:21] line:~% cbacklight --dec 5 --get
intel_backlight: 65.19%
[14:22] line:~%
It was inspired by Sebastian's ybacklight, however it only requires python3 and has no external dependencies.
You can find it in the nsbin repository on https://github.com/telmich/nsbin
Requires you to have sane permissions on the files, but that should be solved by udev or rc.local

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